Poyang and Dongting Lakes, Yangtze River: tributary lakes blocked by main-stem aggradation

During its 6,300-km course from the Tibetan Plateau to the ocean, the Yangtze River is joined by two large lakes: Dongting Lake and Poyang Lake. We explain why these lakes exist. Deglaciation forced the ocean adjacent to the Yangtze mouth to rise similar to 120 m. This forced a wave of rising water surface elevation and concomitant bed aggradation upstream. While aggradation attenuated upstream, the low bed slope of the Middle-Lower Yangtze River (similar to 2 x 10(-5) near Wuhan) made it susceptible to sea level rise. The main stem, sourced at 5,054 m above sea level, had a substantial sedi-ment load to ''fight'' against water surface level rise by means of bed aggradation. The tributaries of the Middle-Lower Yangtze have reliefs of approximately hundreds of meters, and did not have enough sediment supply to fill the tributary accommodation space created by main-stem aggradation. We show that the resulting tributary blockage likely gave rise to the lakes. We justify this using field data and numerical modeling, and derive a dimensionless number capturing the critical rate of water surface rise for blockage versus nonblockage.

Automated summary

This passage explains why two large lakes, Dongting Lake and Poyang Lake, exist along the Yangtze River. It suggests that rising sea levels due to deglaciation caused a wave of water surface elevation and bed aggradation. The blockage of tributaries by the main stem's aggradation resulted in the formation of the lakes.